Marine vessel hull technology has developed over the course of literally thousands of years. In more recent times advances in materials, design, and construction, often assisted by computer modeling, have led to a great diversity of purpose-built and high-performance designs. In parallel with technological advances in the design of vessel hulls has been development of sophisticated propulsion mechanisms, with a great many different known designs for virtually everything from propellers to steering wheels now available for different applications.
Traditionally marine vessel propulsor mechanisms employed one or more propellers driven by an internal combustion engine and supported outboard of the vessel hull, or inboard where a propeller driveshaft penetrates the vessel hull. A gearbox or transmission is typically positioned internally to the vessel hull in inboard configurations, or supported at or aft of the stern for outboards. Various combinations and variations on the basic strategies are also know. In more recent years podded designs have become popular where some of the gearing, driveshafts and the like for rotating propellers is mounted in a pod suspended below the waterline that can itself rotate relative to the vessel hull. In a typical podded propulsor configuration, each pod is associated with an engine, and provides traction for the vessel in addition to steering, with a driveline including a transmission extending between the engines and the pod. U.S. Pat. No. 7,666,040 sets forth one example of a podded azimuthing propulsor design where a propulsor pod is mounted within a so-called tunnel that runs longitudinally down a center of the hull. Among other things, tunnels provide additional surface area that can increase drag and complicate construction of the hull itself.